Alexander Holder lives with his son, Arthur, his niece, Mary, and a small team of servants including Lucy Parr.

He is a respected banker with a reasonably happy home life, but then tragedy strikes and, in his own words, he stands to lose his good name, his diamonds and his son, all in one night.

Mr Holder has lent money to an important personage and as security, he has been given a crown of diamonds.

He takes the crown home and locks it away in a cupboard in his dressing room. Then he ensures that all doors and windows of his house are locked.

But, that same night, he wakes to discover his son holding the damaged crown.

A part of the crown, with three diamonds in it, is missing, and when accused of stealing the missing diamonds, Arthur refuses to explain his actions.

Mr Holder turns him over to the police and goes to Sherlock Holmes for help.

Holmes feels that Arthur must be innocent. Why steal the crown, hide part of it then return to be discovered? And how could he break off the piece anyway?

His suspicions fall on Holder’s other relative, Mary, and he is able to prove that she stole the crown and passed it out of the window to her lover.

Arthur realised what was happening and gave chase to the fleeing man. He managed to grab the crown and, in the struggle, a piece broke off.

He was returning the crown to its rightful place when he was discovered. The thief presumably picked up the broken piece and sold it because Holmes is able to track it down and buy it back.

But in the meantime, Mary has disappeared, probably to join her lover, the thief. Knowing the man for what he truly is, Holmes thinks this will be sufficient punishment for Mary.